A photosensitive resin plate for the manufacture of a relief printing plate is preferably developable with water rather than organic solvents for various reasons such as easiness of handling, health of the working people, safety, and avoidance of environmental pollution. On printing with a relief printing plate resulting from the photosensitive resin plate, it is also very desirable to be able to use water based inks, because oil based inks tend to mist and hence to cause health problems. In addition, the use of water based inks is favored in that the resulting print will not show through the printed paper from one side to the other and does not tend to rub off on the fingers.
There are various known photosensitive resin plates. The photosensitive resin compositions for those conventional photosensitive resin plates are based on liquid unsaturated polyesters, polyvinyl alcohols, water soluble polyamides, cellulose acetate succinates, alcohol soluble polyamides, etc. All these materials, however, suffer from significant disadvantages. For instance, the liquid unsaturated polyesters are inconvenient to handle and necessitate the use of an alkaline solution or a special air knife for developing. The polyvinyl alcohols and the water soluble polyamides have extremely low resistance to water, and consequently water based inks are not usable. The cellulose acetate succinates require the use of an alkaline solution for development, and the alcohol soluble polyamides require the use of an inflammable alcohol.
U.S. Pat. No. 3,801,328 discloses a water developable photopolymerizable composition for preparation of a photosensitive resin plate, said composition comprising unsaturated ethylenic monomers, a photo-polymerization initiator and a partially saponified polyvinyl acetate. This composition has been found to be developed very satisfactorily with water to give a relief printing plate. However, the water resistance of this relief printing plate at the surface is low, which in turn precludes its use with a water based ink.